So as to comply with the strict current legal guidelines and emission regulations, the exhaust gas of internal combustion engines of motor vehicles must be specially handled during emission. As an example, the exhaust is removed from the exhaust gas system, cooled down and once again fed back for new combustion. The heat exchangers for the thermal treatment of the exhaust gas, in particular for the cooling of the exhaust gas, are also indicated as exhaust gas heat exchangers.
In the state of the art, finned heat exchangers are employed as exhaust gas heat exchangers, which are perfused by exhaust gas and coolant. Cooling water is predominantly used for the cooling of the exhaust gas flow.
Exhaust gas heat exchangers according to the state of the art feature fins that are embossed or reshaped from sheet metal, which are inserted in a sheet metal housing and which are welded to the same. The exhaust gas perfuses the inside of the housing with the fins and exchanges the heat through the fins to the housing, and the coolant flows along the outside of the housing and absorbs the heat from the exhaust gas flow. One or a multitude of these housings one on top of the other form the so-called radiator core, which is surrounded by an outer housing for the cooling water flow.
This is furthermore a differentiation of heat exchangers depending on the type of direction of the exhaust gas flow. Therefore, as an example, I-throughputs, U-throughputs and S-throughputs are known in exhaust gas coolers
Moreover, in the state of the art, exhaust gas heat exchangers are known that do not feature the aforementioned rectangular cross section, but rather a round cross section. Shell and tube heat exchangers are employed as exhaust gas heat exchangers with a round cross section.
The use of a round exhaust gas heat exchanger is, for example, desirable when connecting the exhaust gas heat exchanger to a diesel particulate filter.
The heat exchanger tubes, which feature either a round or an oval/rectangular cross section and are sufficiently smaller in dimension when compared to the housing, can be arranged in such a way that the cooler cross section can be fully exploited and a larger exchange surface can be achieved.
There are also spiral heat exchangers that are known in the state of the art, which are likewise commonly employed for heat exchange between liquids.
Spiral heat exchangers comprise two flow channels, which are separated by a wall. This wall is rolled up, according to which the heat exchanger respectively features both an entrance and outlet in the outer housing as well as in the inner core. Normally, spiral heat exchangers are built up using the countercurrent principle. The one medium flows from the outside to the inside in a spiral shape, whereas the second medium flows countercurrent from the inside to the outside.
A spiral heat exchanger of the aforementioned type results, for example, from EP 1214558 B1.
A spiral heat exchanger is moreover known from EP 2251630 B1, which features a spiral body that is made up of at least two spiral metal sheets, which are coiled to create the spiral body. The means of manufacture of this type of spiral heat exchanger occurs through coiling. On the basis of the fashion of manufacturing of this type of heat exchanger, these are also defined as coiling heat exchangers.
The multitude of requirements asked of exhaust gas heat exchangers are still not fully satisfied by the state of the art.
If one of the specifications for an exhaust gas heat exchanger is the need for a round cross section, then the current state of the art using a shell and tube heat exchanger is not ideal. Shell and tube heat exchangers have a limited heat exchanging surface. The possible exchange performance when related to the volume, in particular when related to the installation space, is frequently not sufficient.
From this point of view, the concept of a finned heat exchanger is to be preferred. The same offers a large heat exchanger surface in relation to the volume. A disadvantage is, however, the exploitation of the cooling cross section. To be able to make good use of the cooling cross section, it would be necessary to employ rib channels of varying widths, which would lead to a large number of different components in the manufacture of the heat exchanger. This concept thereby leads to a large technical manufacturing expense, as regards the production and logistics for the components. This correspondingly has a negative impact on the costs.
The use of a standardized channel width would reduce the number of different components to the customary scope, however the exploitation of the cross sectional surface would still be very poor and even worse than in a shell and tube concept. Furthermore, an appropriate coolant flow would be difficult or impossible to achieve in this concept.
The spiral cooler concept would in principle supply a good exploitation of the cross section, however, the use of fins in the gas flow is very difficult to accomplish. Beyond this, there is also a problem with the loss in gas-side pressure. The gas flow cross section is small in relation to the cooling volume and the flow length very large. A further disadvantage consists in the position of the water-gas connections, which do not correspond with generally preferred connections. A spiral heat exchanger is thereby preferred when using the same media, in particular when exchanging heat from liquid to liquid.
An exhaust gas heat exchanger in a coiled execution results from US 2011/0223067 A1.The exhaust gas heat exchanger features tubes laid out in a meandering shape, which are connected to ribs that are transverse to the longitudinal axis. The tubes are then coiled, which results in the heat exchanger package. A disadvantage to this concept is the realization of the thermal distribution, which is only unsatisfactorily solved through the point-shaped contacts between the ribs and the tubes.